Acrylic resins have been widely used, for example, as materials for various parts of electronics products, household appliances, office automation appliances, etc. because of their excellent transparency and stiffness.
However, since the acrylic resins are easily electrified by friction or the like because of their high surface resistivity, they are disadvantageous, for example, in that they are deteriorated in appearance by adhesion of rubbish or dust, or that they bring about an undesirable situation by electrostatic electrification in parts of electronic equipments, etc. Therefore, it is desirable to develop a material having not only the excellent characteristics of the acrylic resins, but also antistatic properties.
As a method for imparting antistatic properties to the acrylic resin, there is well known, for example, a method of kneading a surfactant with the acrylic resin, or applying a surfactant on the surface of the acrylic resin. However, according to such a method, imparting permanent antistatic properties is difficult because the surfactant present on the surface is easily removed by water washing, friction or the like.
As methods for imparting permanent antistatic properties, there have been disclosed, for example, (1) a method of kneading a vinyl copolymer having a polyoxyethylene chain and a sulfonate, carboxylate or quaternary ammonium salt structure, with an acrylate resin (Japanese Patent Unexamined Publication Nos. 55-36237 and 63-63739), (2) a method of kneading a polyether ester amide with a methyl methacrylate-butadiene-styrene copolymer (an MBS resin) or a methyl methacrylate-acrylonitrile-butadiene-styrene copolymer (an MABS resin) (Japanese Patent Unexamined Publication No. 62-119256), and (3) a method of adding a polyamide elastomer, a modified vinyl polymer having at least one functional group such as carboxyl group, epoxy group or hydroxyl group, and optionally a rubber graft copolymer to an acrylate resin to obtain a permanently antistatic resin which is free from exfoliation and excellent in surface gloss (Japanese Patent Unexamined Publication No. 1-308444). In addition, there has also been disclosed, for example, (4) a method of kneading a polyether block amide with an acrylate resin (Japanese Patent Unexamined Publication No. 64-90246).
However, in the method described in (1) above, the vinyl copolymer blended is a special vinyl monomer and hence is expensive, and the production cost of an acrylate resin composition obtained by blending the vinyl copolymer is, of course, unavoidably raised. Moreover, in particular, the method disclosed in Japanese Patent Unexamined Publication No. 55-36237 is disadvantageous, for example, in that heat resistance and the like, which are characteristic of the acrylate resin, are deteriorated because the amount of the vinyl copolymer that is blended is large. On the other hand, in the method described in (2) above, the transparency of the resulting composition is maintained by adjusting the difference in refractive index between the noncrystalline polyether ester amide and the MBS resin or the MABS resin to 0.02 or less, so that the degree of freedom of their combination is low. Furthermore, this method is disadvantageous in that when a poly(methyl methacrylate), a typical acrylic resin, is used, the difference in refractive index is difficult to adjust to a value in a desired range, so that the transparency is apt to be deteriorated.
The antistatic resin described in (3) above is obtained by adding a modified vinyl polymer having at least one specified functional group to a composition of an acrylate resin and a polyamide elastomer substantially incompatible therewith, to improve the compatibility, and thereby preventing exfoliation and imparting an antistatic effect. But, the antistatic resin is not always sufficiently transparent. In addition, the transparency of the antistatic resin described in (4) above is not satisfactory for practical purposes, judging from the value of the transmittance for whole light.
Acrylic resins are markedly characterized by their excellent transparency, but when other high-molecular weight compounds are kneaded with the acrylic resins to impart permanent antistatic properties to the acrylic resins, the compatibility between the acrylic resins and the other high-molecular weight compounds is poor, so that the transparency is often deteriorated. Even if a product having a good transparency can be obtained, sufficient antistatic effect cannot be obtained or the heat resistance is deteriorated. Moreover, when a high-molecular weight compound having a complicated structure is produced and then used for its exhibition of a sufficient antistatic effect, the production cost is raised and there cannot be obtained an acrylic resin having general-purpose properties, i.e., is not expensive, and has antistatic properties, that is entirely satisfactory for practical purposes.
Under these circumstances, there has been a desire to develop an acrylic resin composition which has excellent permanent antistatic properties, is inexpensive and is good in transparency.
The present inventors investigated acrylic resin compositions having excellent antistatic properties and transparency and previously found that a polyamide-imide elastomer having a low content of hard segments has good compatibility with acrylic resins, and is finely dispersed thereinto to give a transparent composition having excellent antistatic properties. The present inventors have disclosed this finding in Japanese Patent Unexamined Publication No. 2-255753. The polyamide-imide elastomer, however, is light-yellow and it is not always satisfactory because an acrylic resin containing the polyamide-imide elastomer is colored light-yellow. Furthermore, the polyamide-imide elastomer is not always satisfactory because when said acrylic resin composition is immersed in water, its transparency is deteriorated.